This invention relates to an improvement in an automatic film advancing system for a photographic camera, wherein the film is advanced by one frame immediately following each shutter closing after photographing.
Recently, small-sized cameras have widely used the so-called 110 type film. This film is contained in a small cartridge and has a series of perforations, each perforation engaging in turn with a sprocket inside the cartridge, a perforation being provided for each picture frame of 13mm .times. 17mm. Some of such cameras have been provided with an automatic film advancing system comprising a motor and a controlling circuit.
In the conventional automatic film advancing system, the controlling circuit switches on the motor feeding circuit upon closing of shutter blades after photographing, and switches off the motor feeding circuit when the film is advanced exactly by one frame to thereby stop the film advancing. The advance of film by one frame is detected by the motion of a lever of a switch in the controlling circuit, a moving end thereof being engaged to each of the perforations in turn. In such system, the switch is designed to be turned "off" when the moving end of the lever comes to a predetermined position. However, the 110 type film has no perforation at the end part of its roll. Therefore, if a user inadvertently continues to cause the film advancing in such end part of the roll, the moving end of the lever can not precisely come to the predetermined position.
Resultantly, the switch continues to be closed forever, thereby continuing to energize the motor. In such case, the motor current continues to flow notwithstanding the fact that film, and hence the motor, can not move. Therefore the motor is undesirably overloaded until the batteries are worn out, thereby possibly damaging the motor and wasting the batteries. Additionally, similar overcurrent in the stopped motor may occur when the film is accidentally caught.